Class AuthorizedKeysManhole

This Manhole accepts ssh connections, and requires that the
prospective client have an ssh private key that matches one of the public
keys in our authorized_keys file. It is created with the name of a file
that contains the public keys that we will accept.

__init__(self,
port,
keyfile)(Constructor)

port (string or int) - what port should the Manhole listen on? This is a strports
specification string, like 'tcp:12345' or
'tcp:12345:interface=127.0.0.1'. Bare integers are treated as a
simple tcp port.

keyfile - the name of a file (relative to the buildmaster's basedir) that
contains SSH public keys of authorized users, one per line. This
is the exact same format as used by sshd in
~/.ssh/authorized_keys .